a) Field of the Invention
The invention relates to a variable length steering spindle for steering mechanisms of motor vehicle. The steering spindle including an outer sleeve-form profile with a cross section departing from the circular form, and an inner profile with a cross section departing from the circular form, which can be slid with an end section into the outer profile, wherein the inner circumferential contour of the outer profile. The outer circumferential contour of the inner profile are formed at least partially by arcuate sections and, toward the gap space between the outer profile and the inner profile, these arcuate sections form preferably alternately convex and concave sections of the outer profile as well as also of the inner profile. The convex sections of the outer profile are disposed at least partially opposite the concave sections of the inner profile, and/or the concave sections of the outer profile are disposed at least partially opposite the convex sections of the inner profile. The spindle also included a slide sleeve disposed in the gap space, which sleeve is held with respect to one of the two profiles torsion-tight and nondisplaceable in the longitudinal direction and which, together with the profile holding the slide sleeve, is displaceable with respect to the other profile in the longitudinal direction, however, is substantially torsion-tight.
b) Description of Related Prior Art
Such a variable length steering spindle is disclosed in U.S. Pat. No. 6,149,526 A. The slide sleeve disposed in the gap space between the inner and the outer profile is along its circumferential contours only sectionwise and alternately in contact on the walls of the profile delimiting the gap space. It is alternately in contact on convex sections of the inner profile and on concave sections of the outer profile. Herein the play necessarily present between the parts is compensated, wherein upon a rotational movement of the steering wheel a steering resistance sets in that is virtually free of play. The necessarily present play is no longer perceived as such by the motor vehicle driver actuating the steering since the slide sleeve is prestressed with respect to the outer profile. Nevertheless, the values predetermined for the axial displaceability of the profiles can be reliably maintained over a longer period of time. One disadvantage of this construction is that with progressive decrease of the tolerated actual play between the inner and the outer profile, which is desirable in practice, the so-called “slip-stick motion” may occur between the slide sleeve and the profile displaceable with respect to it. The sliding during a longitudinal displacement is thus no longer continuous but rather a rattling movement results, which can be perceived on the steering wheel and can also lead to undesirable noise. Such a slip-stick can occur not only during a length adjustment of the steering column but also with vehicle distortion when driving through curves.
In addition to slide guidings between steering spindle parts, thrust guides with rolling bodies acting between the shaft parts are also disclosed, for example in DE 37 30 393 C2, DE 101 23 413 A1, DE 198 24 477 A1, EP 1 652 748 and EP 1 065 397. Via these rolling bodies, the torques acting between the steering spindle parts must also be transmitted. In order to be able to also absorb high steering forces, these constructions are complex with respect to the development of the raceways for the rolling bodies and appropriate numbers and sizes of rolling bodies must also be employed, which must work nearly free of play. To some extent are also provided elements resiliently supporting the rolling bodies with respect to the one profile, which elements prestress the rolling bodies against the other profile.
EP 1 070 865 A2 discloses a linear roller bearing, which is not of the same class, for the transmission of torques, which bearing is developed with continuous ball raceways. The continuous ball raceways are developed in a cage disposed between the outer and the inner profile. For the playfree prestress of the profiles against one another, a prestress means acting onto the balls is provided which is formed in particular by a raceway section located in the load zone and formed spring-resiliently on one of the oppositely located wall sections of the profiles. When introducing a torque acting between the profiles, the wall section can spring-in so far that the oppositely located wall sections of the profiles move toward one another until they come into contact or clamp in a section of the cage located between them. Of disadvantage in this device is inter alia the implementation, which is complex due to the continuous ball raceways. In this construction it is also not readily possible to attain a very small overall play between the inner and the outer profile until the wall sections associated with one another are in contact with one another or clamp a section of the cage between them, and in such a load case the displaceable guidance between the inner and the outer profile is restricted.